The invention relates to an electron beam drawing apparatus for exposing a fine pattern onto a semiconductor or a mask mother disk.
An example of conventional electron beam drawing apparatuses has been disclosed in JP-A-8-320570. According to the above Official Gazette, an upper edge of an objective lens of an electron beam column is fixed to a sample chamber by beams in order to prevent the electron beam column from causing a rolling due to external vibration or vibration in the apparatus, particularly, movement of a sample stage. Thus, a lower edge of the objective lens is fixed to the sample chamber and the rolling is prevented by 2-point supporting.
Another example of the conventional electron beam drawing apparatuses has been disclosed in JP-A-2000-138279. According to the above Official Gazette, in order to miniaturize a stage and realize a lightweight thereof, the apparatus has a structure such that a flange portion of a projection optical system is provided for a column fixed base plate, leg portions of a frame are fixed to the column fixed base plate, and a reticule base is attached to the frame. Further, a pole portion is on a vibration isolating base which supports corner portions of the column base plate. The pole portion is projected to a drawing area from the column base plate and a hole for exposure is formed in a mid position of the pole portion.
According to the electron beam drawing apparatus disclosed in JP-A-8-320570, a technique such that even if out-of-plane rigidity of a top plate is not increased, by supporting two points of the lower edge and the upper edge of the objective lens of the column to the sample chamber, rotational vibration of the column can be reduced has been disclosed. However, by experimental studies by the present inventors et al., it has been found that in a rotational vibrating mode which is caused in the column by the movement of the stage, an out-of-plane deformation of the top plate is a main factor. Therefore, unless the out-of-plane deformation of the top plate is restricted, it is difficult to reduce the rotational vibration of the column.
If the out-of-plane deformation of the top plate is restricted and two points of the lower edge and the upper edge of the column are supported, the rotational vibration of the column which is caused at the time of the movement of the stage can be reduced. However, the sample chamber is also increased in size in association with an enlargement of the stage. With respect to the large top plate, it is difficult to increase the out-of-plane rigidity. That is, according to the above Official Gazette, the out-of-plane deformation of the top plate is not sufficiently considered.
The electron beam drawing apparatus is operated by setting the inside of the sample chamber into a vacuum state. At this time, a large load acts on the top plate of the sample chamber by a negative pressure (hereinafter, referred to as a vacuum negative pressure) between the atmospheric pressure and the vacuum pressure in the sample chamber. Since the load which is caused by the vacuum negative pressure increases in proportion to a size of top plate, if the out-of-plane rigidity of the top plate of the sample chamber is insufficient, the top plate sinks in the vertical direction and a large deformation is caused at the center of the top plate provided with the column.
According to JP-A-2000-138279, although the projection optical system has been provided on the column fixed base plate, in an exposing apparatus disclosed in this Official Gazette, since the projection optical system is not supported at two points, the foregoing problem occurs when the column fixed base plate enlarges. Nothing is considered with respect to such a problem.
Further, when the stage is accelerated or decelerated and moved in the electron beam drawing apparatus, an inertial force is generated and its reactive force is propagated to the sample chamber. Thus, the column standing upright on the top plate of the sample chamber is vibrated from a foundation. If the out-of-plane rigidity of the top plate supporting the column is small, a natural frequency of the column also decreases. When the natural frequency of the column decreases to a frequency component of the reactive force of the stage, the column is vibrated by the stage reactive force. By the studies of the present inventors et al., it has been found that the vibrating mode of the column in this case is a rotational vibrating mode in which the column is a rigid body and the top plate supporting the column is deformed.
When the rotational vibrating mode occurs, relative displacement in the horizontal direction is caused between the column and a sample, a positional deviation of an electron beam is caused on the sample, and positioning precision of the electron beam deteriorates. To avoid such a problem, if a high rigidity structure in which the column is provided on the top plate of the sample chamber and the rigidity in the out-of-plane direction of the top plate is raised is used, a weight of top plate increases and the maintenance performance of the stage deteriorates.
The invention is made in consideration of the problems of the foregoing conventional techniques and it is an object of the invention to improve the reliability of drawing even in an electron beam drawing apparatus having a large sample chamber. Another object of the invention is to prevent a rotational vibration of a column even if a stage is moved in an electron beam drawing apparatus. Still another object of the invention is to improve a throughput in an electron beam drawing apparatus. Further another object of the invention is that the occurrence of a distortion in an electron lens provided in a column is prevented by restricting displacement in the vertical direction of the column. Further another object of the invention is to accomplish at least one of those objects.
According to the first aspect of the invention to accomplish the above objects, there is provided an electron beam drawing apparatus having a sample chamber in which a stage to set a sample has been enclosed, a fixed base plate for holding the sample chamber, and a column having therein an electron gun for irradiating an electron beam to the sample, comprising: a frame which sets the column onto a top plate in an upper portion of the sample chamber and has leg portions extending from corner portions of the fixed base plate to a center; a supporting apparatus held on the frame; and positioning means for adjusting a gap between the column and the supporting apparatus.
In the first aspect, vibration sensors are attached to side surfaces of an upper portion and a lower portion of the column, the positioning means has an actuator, and control means for controlling the actuator on the basis of signals detected by the vibration sensors can be also provided. There are four leg portions of the frame, the supporting apparatus can be arranged at positions where an outer circumference of the column is divided into almost four equal parts, and the control apparatus can synchronously control the actuators arranged symmetrically with respect to an axis of the column. Further, it is desirable that the control means controls in a manner such that when one of the actuators arranged symmetrically is executing the tensile operation, the other actuator executes the contracting operation.
According to the second aspect of the invention to accomplish the above objects, there is provided an electron beam drawing apparatus having a stage on which a sample is set and which is moved in the horizontal direction, a sample chamber for enclosing the stage, a fixed base plate for mounting the sample chamber, and a column which is arranged in an upper portion of the sample chamber and has therein an electron gun, an electron lens for shaping and converging an electron beam emitted from the electron gun, and a deflector for deflecting the electron beam, comprising: pillar members provided for the fixed base plate; a frame which is fixed to the pillar members and arranged around the column; and a plurality of supporting apparatuses which are fixed to the frame and support the column.
In the second aspect, the pillar members can be integrated with the sample chamber, both ends of the supporting apparatuses are coupled with the column and the frame, respectively, and each of the supporting apparatuses can include a coupling member which is rigid in the rectilinear direction coupling the column and the frame and is soft in at least one of the directions which cross perpendicularly the rectilinear direction. The supporting apparatus includes a direct acting actuator for applying a dynamic load in the horizontal direction of the column, and the electron beam drawing apparatus can have: vibration sensors which are arranged in an upper portion and a lower portion of the column and measure acceleration; and a controller for controlling the direct acting actuator so as to reduce a relative amount of the acceleration of the vibration sensor.
According to the invention having such aspects, since the frame for mounting the supporting apparatuses is fixed to the pillar members having high rigidity, the frame can support the column in its upper portion in the horizontal direction without being influenced by the out-of-plane deformation of the top plate due to the vacuum negative pressure. Thus, a natural frequency of the column can be increased merely by supporting the column at two points of the lower portion and the upper portion of the column, and the rotational vibration of the column can be reduced against the movement reactive force of the stage. Since the direct acting actuator is controlled so as to reduce the relative amount of the acceleration by using the acceleration vibration sensors arranged in the upper portion and the lower portion of the column, the rotational vibration of the column can be further suppressed.
Since the coupling member which is rigid in the axial direction and soft in the shearing direction is provided, the rotational vibration of the column is reduced. Moreover, since a situation such that the top plate sinks due to the vacuum negative pressure and the vertical direction of the column is deviated or a situation such that the electron lens generates heat and the column is extended in the vertical direction is not restricted, shaping performance and convergence of the electron beam are improved and a drift of the electron beam can be prevented.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.